This application claims the priority of 198 40 629.0-13, filed Sep. 5, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a drive assembly for a vehicle having an internal-combustion engine for delivering driving energy, an exhaust gas turbocharger which has a turbine and a compressor, with the turbine being driven by exhaust gases of the internal-combustion engine and the compressor being driven by the turbine, and an air guiding system which feeds fresh air to the compressor in which it is compressed to form charge air. The air guiding system guides the charge air from the compressor to the internal-combustion engine.
In known drive assemblies, an exhaust gas turbocharger is normally used for increasing the power of an internal-combustion engine. This exhaust gas turbocharger has a turbine driven by exhaust gases of the internal-combustion engine and a compressor driven by the turbine. Fresh air, which is normally taken in from the atmospheric environment of the vehicle via an air filter, is compressed to form charge air which is then supplied from a compressor to the internal-combustion engine for the combustion. As the result of the compression, a larger flow rate is obtained which permits an increase of the power of the internal-combustion engine.
Because the exhaust gas turbocharger of a drive assembly is normally designed for the full-load operation at high rotational engine speeds, the exhaust gas turbocharger can cause only a relatively low compression of the fresh air at low rotational engine speeds. In such a low rotational speed range of the internal-combustion engine, a power increase can hardly be achieved with the exhaust gas turbocharger. The compressor will generate a sufficient supercharging only at higher rotational speeds. By way of the increased air flow rate and the correspondingly enlarged fuel flow rate, this supercharging causes, on one hand, a power increase of the internal-combustion engine and, on the other hand, an increased exhaust gas temperature and a raised exhaust gas pressure, whereby the power output of the turbine is considerably increased. Because of this feedback, the internal-combustion engine can rapidly supply a high power as soon as the turbocharger "responds"; i.e., as soon as a sufficient supercharging takes place by the compressor. Normally, a so-called "turbohole" exists at low rotational speeds until the turbocharger responds.
In order to improve the efficiency of a supercharged internal-combustion engine also in the range of low rotational speeds, a large number of different suggestions have been made.
For example, U.S. Pat. No. 3,673,797 describes a drive assembly in which the driving power of an internal-combustion engine is increased by a turbine driven by the exhaust gases of the internal-combustion engine. The turbine feeds its driving power into a differential gearing which interacts with the transmission line of the internal-combustion engine. In this manner, the driving power of the internal-combustion engine is increased directly by the driving power of the turbine. This turbine also has, however, a turbohole at low rotational speeds of the internal-combustion engine.
In addition, in this drive assembly, a second differential gearing is arranged in the transmission line driven by the internal-combustion engine and the turbine. By way of the second differential gearing, a compressor is driven which compresses fresh air and feeds it as charge air to the internal-combustion engine. The compressor, which is mechanically driven in this manner, therefore indirectly also increases the driving power of the internal-combustion engine. Such a mechanically driven compressor has no very pronounced turbohole like that associated with an exhaust gas turbocharger so that, also at lower rotational speeds, a power increase can be achieved here by supercharging the engine.
Furthermore, the known drive assembly has another compressor which is driven by the turbine and compresses fresh air which is then supplied either in series to the other compressor or in parallel thereto to the internal-combustion engine. A drive assembly constructed in this manner can be implemented only at very high expenditures.